A392358 Decimal expansion of (2 - sqrt(2*sqrt(2) - 2)/(2^2))^2.

3, 1, 4, 1, 5, 9, 6, 9, 7, 4, 1, 7, 2, 1, 8, 2, 1, 9, 8, 4, 9, 1, 4, 9, 5, 5, 7, 4, 8, 8, 1, 2, 7, 5, 1, 2, 0, 5, 8, 0, 8, 2, 8, 2, 2, 7, 4, 5, 5, 8, 1, 8, 3, 2, 3, 9, 7, 0, 5, 6, 5, 8, 2, 8, 2, 6, 7, 2, 4, 1, 1, 5, 3, 3, 4, 0, 8, 6, 6, 7, 9, 6, 6, 7, 3, 4, 9, 4, 8, 0

Offset

1,1

Comments

This expression, using only the digit 2, is an approximation to Pi accurate to 6 digits.

Links

Paolo Xausa, Table of n, a(n) for n = 1..10000

Heinrich Hemme, Die Quadratur des Kreises, Hemmes mathematische Rätsel, 16.04.2020, Spectrum (in German).

Wikipedia, Approximations of pi.

Index entries for algebraic numbers, degree 4.

Index entries for sequences related to the number Pi.

Formula

Equals (2 - A388753/4)^2.

Minimal polynomial: 4096*x^4 - 63488*x^3 + 385152*x^2 - 1086496*x + 1181569. - Amiram Eldar, May 26 2026

Example

3.1415969741721821984914955748812751205808282274558...

Mathematica

First[RealDigits[(2 - Sqrt[2*Sqrt[2] - 2]/4)^2, 10, 100]]

Prog

(PARI) (2-sqrt(2*sqrt(2)-2)/4)^2 \\ Charles R Greathouse IV, May 18 2026

Crossrefs

Cf. A000796, A388753.

Sequence in context: A374322 A068079 A152042 * A057466 A187079 A086183

Adjacent sequences: A392355 A392356 A392357 * A392359 A392360 A392361

Keyword

nonn,cons,easy

Author

Paolo Xausa, Feb 10 2026

Status

approved